The present invention relates, in general, to an apparatus and method for linking data processors and peripheral devices and, more specifically, to an apparatus and method for linking devices over high speed fiber optic links.
Data centers are typically linked together so that data may be shared by multiple customers, who are remotely located from each other. The customers, such as banks and credit card issuers, need high speed connectivity between their server systems and mainframe systems to provide quality service and maximize their investment in information management. Applications that require such high speed connectivity include transaction co-processing, massive file transfers for decision support, archival databases for disaster recovery and transaction reporting requirements.
Referring to FIG. 1, there is provided a data processing interconnection system 10 of the prior art. An example of system 10 is an IBM data processing interconnection system known as Enterprise Systems Connection (“ESCON”) (Trade Mark). “ESCON” is an interconnection system using fiber optic technology. Fiber optic links, such as links 14, 18, 22 and 26 create a local area network extending for kilometers among numerous systems, such as host processor 12, control units 24 and 28.
In “ESCON” architecture multiple systems may communicate with each other via channel-to-channel communications. For example, multiple mainframe systems may communicate channel-to-channel or gain access to multiple devices or communication control units. Referring to FIG. 1, channel directors 16 and 20 are capable of employing any-to-any, point-to-point switching and may make numerous physical connections between each other and peripheral devices. As shown, channel director 20 connects four fiber optic links 18 from channel director 16 with two fiber optic links 22 and two fiber optic links 26, each respectively branching to control units 24 and 28.
Although not shown in FIG. 1, channel director 20 or 22 may have as many as 256 optical ports to support as many as 128 “ESCON” connections simultaneously and without contention. Each channel director includes a set of quad port adapters (QPAs). Each QPA handles the “ESCON” input or output data with four individual ports. The ports include either multi-mode optical transceivers or single-mode optical transceivers. Two QPA modules are shown in FIG. 1, namely QPA module 17 and QPA module 19.
A more detailed arrangement of QPAs is shown in FIG. 2. As illustrated, multiple QPAs 17a-17n are coupled to switch matrix 15 within channel director 16. Each QPA has four output/input ports (27a-27n) for providing up to four connections to remote devices. Switch matrix 15 provides the switching fabric to connect any one ESCON port to any other ESCON port. For example, two ports (27a) in QPA (1) are connected to two ports (27b) in QPA (2). In this manner, channel director 16 provides multiple interfaces and channel-to-channel switching among multiple devices.
A physical link between two points may consist of two fibers, one for transmitting and one for receiving. Information on the link is transmitted in a special 10-bit code, giving an instantaneous link rate of 20 megabytes per second or 200 megabits per second. After deducting for control (e.g., pacing bytes) and data encoding overhead, a channel data rate for real application data of 17 megabytes per second is achieved.
Data are transmitted in the form of packets of characters called frames. Each character contains 10 bits when use is made of the 8 of 10 code to provide a dc balanced code. The frames can vary in size from 12 bytes to 1036 bytes. Each frame includes both the frame source address and its destination address. The addresses are used to route frames through the network. A switch matrix controller (not shown) within the channel director examines the destination address and dynamically connects the port receiving the frame to the destination port.
“ESCON” technology permits a maximum link rate of 200 megabits/sec between channel directors. The physical links are one-to-one and one port is required at each channel director to support both sides of the link. This one-to-one arrangement can become expensive, because valuable ports and fiber are consumed to support communications between channel directors. Typically, a user must lease one fiber optic link for every port in a control unit. More detail of “ESCON” architecture is provided by S. A. Calta, et al. in “Enterprise Systems Connection (ESCON) Architecture-System Overview”, July 1992, (IBM Journal Res. Development, Vol. 36, No. 4) and is incorporated herein by reference.
A need still exists for an apparatus and method for communicating between channel directors that does not require a one-to-one physical link per port. A need also exists for an interface device that may simultaneously support connectivity from multiple “ESCON” ports onto a single fiber link to reduce the cost of leasing fiber links.